The present invention relates to a polyazo compound or a salt thereof, and a dye-based polarization film containing the same.
Dye-based Polarization films are produced by adding a dye covering the desired wave-length region as a polarization element into a polarization film substrate such as a drawn and oriented polyvinyl alcohol-based film, an oriented polyene-based film produced by de-hydrochloric acid of a polyvinyl chloride film or dehydration of a polyvinyl alcohol film, and the like. As an example of dyes covering the region of from 500 to 580 nm, a polyazo compound represented by the following formula is known (JP-A-5-295281, Example 1). 
However, polarization films produced by using the known polyazo compound mentioned above are not completely sufficient yet from the view points of initial polarization ability, etc.
The object of the present invention is to provide a polyazo compound usable for producing a dye-based polarization film covering the region of from 500 to 580 nm and particularly excellent in Initial polarization ability.
The present inventors have conducted extensive studies, and, resultantly, they have found that a specific polyazo compound or salt thereof attains the above-mentioned object. Thus, the present invention was completed.
Namely, the present invention provides a polyazo compound or salt thereof represented by the following formulae (I) or (II): 
wherein,
A represents a phenyl having sulfo and/or carboxyl and optionally having a lower alkyl or lower alkoxy, or a naphthyl having 1 to 3 sulfos,
R1 to R6 are the same or different and represent hydrogen, lower alkyl or lower alkoxy,
m and n each independently represents 0 or 1.
R7 represents hydrogen or sulfo,
D and E each independently represents xe2x80x94NHCOxe2x80x94 or xe2x80x94Nxe2x95x90Nxe2x80x94,
G represents xe2x80x94CH2xe2x80x94, alkylene having 2-4 carbon atoms, phenylene or xe2x80x94CHxe2x95x90CHxe2x80x94,
and R8 represents sulfo, carboxyl or lower alkoxycarbonyl, provide that, when G represent phenylene, n is 1.
A in the above-mentioned formula (I) represents a naphthyl having 1 to 3 sulfos or a phenyl having sulfo and/or carboxyl and optionally having a lower alkyl or lower alkoxy. The lower alkyl or lower alkoxy is preferably a linear or branched group having 1 to 4 carbon atoms Specific examples of the lower alkyl include methyl, ethyl, propyl and the like. Specific examples of the lower alkoxy include methoxy, ethoxy, propoxy and the like
As the phenyl represented by A, a phenyl having sulfo and/or carboxyl wherein the total number of sulfo and carboxyl is 1 or 2 is preferred. Examples of the phenyl include 2-, 3- or 4-sulfophenyl, 2-, 3- or 4-carboxyphenyl, 2,4- or 2,5-disulfophenyl, 3,5-dicarboxyphenyl, 2-carboxy-4- or -5-sulfophenyl, 2- or 3-methyl-4-sulfophenyl, and the like. Among them, a phenyl having sulfo is preferable from the view points of dyeing and 4-sulfophenyl is particularly preferable.
Examples of the naphthyl represented by A include 5-, 6-, 7- or 8-sulfo-2-naphthyl, 4-, 5-, 6- or 7-sulfo-1-naphthyl, 1,5-, 6,8-, 4,8-, 5,7- or 3,6-disulfo-2-naphthyl, 3,6- or 4,6-disulfo-1-naphthyl, and 1,5,7-, 3,6,8- or 4,6,8-trisulfo-2-naphthyl and the like. Among them, naphthyls having 2 to 3 sulfos are preferable from the view points of dyeing, and disulfo-2-naphthyls such as 1,5-, 6,8-, 4,8-, 5,7- or 3,6-disulfo-2-naphthyl and the like are particularly preferable.
R1 to R6 each independently represent hydrogen, lower alkyl or lower alkoxy. The lower alkyl or lower alkoxy is preferably a linear or branched group having 1 to 4 carbon atoms. Specific examples of the lower alkyl include methyl, ethyl, propyl and the like. Specific examples of the lower alkoxy include methoxy, ethoxy, propoxy and the like.
R1 to R6 preferably represent hydrogen or methyl.
R7 represents hydrogen or sulfo, and preferably hydrogen.
R8 represents sulfo, carboxyl or lower alkoxycarbonyl, and preferably lower alkoxycarbonyl, such as xe2x80x94COxe2x80x94OCH3. The lower alkoxy in the lower alkoxycarbonyl is preferably a linear or branched group having 1 to 4 carbon atoms. Specific examples of the lower alkoxy include methoxy, ethoxy, propoxy and the like. As R8, methoxycarbonyl and ethoxycarbonyl are preferable, and particularly methoxycarbonyl is preferable.
G represents xe2x80x94CH2xe2x80x94, alkylene having 2-4 carbon atoms, phenylene or xe2x80x94CHxe2x95x90CHxe2x80x94. Among them, xe2x80x94CH2xe2x80x94 and ethylene are preferable, and ethylene is particularly preferable
m and n each independently represents 0 or 1, provide that, when G represent phenylene, n is 0.
A polyazo compound of the formula (I) or a salt thereof can be produced, for example, by the following method.
First, a compound of the following formula (VII): 
wherein, R1-R6, A and D are as defined above are diazotized by reacting with sodium nitrite in an acidic aqueous medium under a condition of 5 to 4xc2x0 C.
Then, the resulted diazo compound is reacted with an amide compound of the following formula (III): 
wherein, R7, R8, E, G and n are as defined above to obtain the polyazo compound of the formula (I) or a salt thereof.
A compound of the formula (VII) wherein m=1 or a salt thereof can be produced, for example, by the following method.
First, an azo compound of the following formula (IV): 
wherein, R1-R4, A and D are as defined above, is diazotized by reacting with sodium nitrite in an acidic aqueous medium under a condition of 5 to 40xc2x0 C. The resulted diazotized compound is reacted with an aniline compound of the following formula (V): 
wherein, R5 and R6 are as defined above, in an aqueous medium under conditions of 5 to 40xc2x0 C. and pH from 6 to 11, to obtain a compound of the formula (VII) wherein m=1 or a salt thereof.
A compound of the formula (VII) wherein m=0 or a salt thereof can be produced, for example, by reacting a compound obtained by diazotizing a compound of the following formula (VI): 
wherein, R1, R2, A and D are as defined above, with the above aniline compound of formula (V).
An amide compound of the formula (III) can be produced, for example, by reacting a naphtol compound of the following formula (IIa): 
wherein E, n and R7 are as defined above, with an acid anhydride or acid halide which is capable of; introducing xe2x80x94COxe2x80x94Gxe2x80x94R8 (wherein, G and R8 are as defined above) into xe2x80x94NH2 group in the formula (IIa).
A polyazo compound of the formula (II) or a salt thereof can be produced by changing a polyazo compound of the formula (I) wherein R6 is methoxy to a copper complex thereof according to a conventional method.
Examples of salts of polyazo compound of the formula (1) and salts of polyazo compound of the formula (II) include 
and the like.
As examples of the salt of a polyazo compound (I) and the salt of a polyazo compound (II), alkali metal salts such as a lithium salt, sodium salt and potassium salt, an ammonium salt, and organic amine salts such as an ethanolamine salt and alkylamine salt, and the like are listed. When a polyazo compound of the formula (I) and/or a polyazo compound of the formula (II) is added into a polarization film substrate, a compound in the form of a sodium salt is preferably used.
When a polyazo compound of the formula (I), a polyazo compound of the formula (II) or salt thereof is added into a polarization film substrate to give a polarization film, hue can be modified and polarization ability can be improved by combination with another organic dye. As the organic dye used in this case, any dye can be used as long as it has high dichroism. A polarization film suitably used in a liquid crystal projector can be produced, using a dye excellent in light resistance.
Specific examples of such organic dyes include the following compounds expressed by Color Index Generic Name.
C. I. Direct Yellow 12
C. I. Direct Yellow 28
C. I. Direct Yellow 44
C. I. Direct Orange 26
C. I. Direct Orange 39
C. I. Direct Orange 107
C. I. Direct Red 2
C. I. Direct Red 31
C. I. Direct Red 79
C. I. Direct Red 81
C. I. Direct Red 247
The dye-based polarization film of the present invention can be produced by adding a dichromatic dye comprising a polyazo compound of the formula (I), a polyazo compound of the formula (II) or salt thereof, or a dichromatic dye further comprising other organic dye, into a polymer film, polarization film substrate, by a known method. Examples of this polymer film include polymer films made of polyvinyl alcohol-based resins, polyvinyl acetate resins, ethylene/vinyl acetate (EVA) resins, nylon resin, polyester resins or the like. Examples of the polyvinyl alcohol-based resin herein referred to include a partial or complete saponified polyvinyl acetate, that is polyvinyl alcohol; saponified substances of copolymers of vinyl acetate with other copolymerizable monomers, for example, olefins such as ethylene and propylene, unsaturated carboxylic acids such as crotonic acid, acrylic acid, methacrylic acid and maleic acid, unsaturated sulfonic acids, vinyl ethers, and the like, such as saponified EVA resins; polyvinyl formal and polyvinyl acetal obtained by denaturing polyvinyl alcohol with an aldehyde, and the like. As the polarization film substrate, polyvinyl alcohol-based films, particularly, a polyvinyl alcohol film is suitably used from the standpoints of adsorbing property and orientation property of a dye.
For adding a dichromatic dye into such a polymer film, a method of dyeing a polymer film is usually adopted. Dyeing can be effected, for example, according to the following method. First, a dichromatic dye is dissolved in water to prepare a dye bath. The concentration of a dye in the dye bath is not particularly restricted, but usually selected in the range from 0.0001 to 10% by weight. If necessary, a dyeing aid may be used. For example, it is suitable to use sodium sulfate in an amount of 0.1 to 10% by weight in a dye bath. A polymer film is immersed into the dye bath thus prepared, and dyeing is effected. The dyeing temperature is preferably from 40 to 80xc2x0 C. Orientation of a dye is conducted by stretching a polymer film. As the stretching method, any method such as a wet method, dry method and the like may be adopted, for example. Stretching of a polymer film may be conducted before dyeing or after dyeing.
A polymer film obtained by adding and orientating a dye is subjected, if necessary, to a post treatment such as boric acid treatment and the like according to a known method. Such a post treatment is effected for improving light transmittance, degree of polarization and endurance of a polarization film. Though conditions of the boric acid treatment differ depending on the kind of a polymer film used and the kind of a dye used, the boric acid treatment is generally effected using a boric aced aqueous solution having a concentration of from 1 to 15% by weight, preferably from 5 to 10% by weight at a temperature ranging from 30 to 80xc2x0 C. preferably from 50 to 80xc2x0 C. Further, if necessary, a fix treatment may be together conducted using an aqueous solution containing a cationic polymer compound.
A protective film excellent in optical transparency and mechanical strength can be pasted on one surface or both surfaces of thus obtained dye-based polarization film, to give a polarization plate. The material forming a protective film may be which conventionally used For example, films composed of a fluorine resin such as an ethylene tetrafluoride/propylene hexafluoride copolymer, polyester-based films, polyolefin-based films, polyamide-based films and the like may be used, in addition to cellulose acetate-based films and acrylic films.
The following examples illustrate the present invention further in detail, but should not be construed to restrict the scope of the invention at all. xe2x80x9c%xe2x80x9d and xe2x80x9cpartsxe2x80x9d in the examples are by weight unless otherwise stated.